Magnetically balanced devices, known as intercepter transformers e.g. Wiegand patent U.S. Pat. No. 2,479,656 control the magnitude of a secondary current according to a lesser level of current in a control winding. The underlying principle being orthogonal driving resonance, also known as parametric coupling/power transfer.
An intercepter transformer disclosed in Wiegand patent U.S. Pat. No. 2,740,096 performed the work of a saw-tooth-wave generator (poly-frequency capability). Even further, Wiegand patent U.S. Pat. No. 2,910,654 provided wide-band frequency conversion by means of passive elements. The Paraformer (Wanlass) transformer utilizes a parametric coupling wherein the flux paths of primary-secondary have independent existences and is more closely related to an oscillator. Power transfer is by means of the primary current modulating the secondary inductance. Energy is built up in a series resonant LC "tank" circuit. Frequency modulation of the polar coordinate sensor poly-phase excitation has been shown to have a similar building action i.e. a flaw imbalance triggering an LC resonant circuit into sub-harmonic signal build-up drawing enegry from the orthogonal driving field.
Fundamentals of Polar Coordinates Sensors
The sensing devices contained in the ascending Logue Patents combine (1) orthogonal driving (also known as parametric coupling), (2) a series resonant pick-up coil and capacitor, (3) an annular air gap between pick-up core and driving core, (4) a secondary annular air gap in the pick-up core magnetic circuit, (5) a ramping sine-cosine excitation frequency. These fundamental principles were set forth in Logue U.S. Pat. No. 5,909,118. In FIG. 1, driving toroid 55 is single wound with layer sine-cosine distributions (only one excitation winding 62 and leads Le are shown) for generating a hemispherical shaped effective field. Poly-phase excitation causes angluar motion FR of driving dipole S-N. This driving also couples to pick-up core 88 (a pot core half), and in turn couples the workpiece (not shown). Thus at least two radii of effective flux couples the workpiece, a major hemisphere 71H and a minor hemisphere 71h in FIG. 2. Also complementary hemisphere 71Hc fringes from the opposite side of driving plane S-N.
Principle (1): A plane intersecting a hemisphere at various degrees of latitude reflects a constant axisymmetry to a point on the axis of revolution. This means, "lift-off" and layer spacing variations do not change the flaw waveform signature, only the signal amplitude. Pick-up core 88 may be a conventional pot core half comprising an outer cylindrical pole 86 and a tubular central pole 84 joined by an annular base portion 85. Pick-up coil 90 is wound coaxially in the annular space 79 connected by leads Ls. There is a central bore 93 extending axially the length of core 88. FIG. 2 is a cross-section view of pick-up core 88 illustrating mentioned resonant flux path 71R fringing across air gap 79. An imbalance (asymmetry) in minor driving arc 71h initates the resonant flux path 71R. The indicated "tank" capacitor is not shown in the present drawings for briefness, but the action assumed.
The preferred embodiments of the invention include:
(1) Resonant oscillatory initation is made more dependent on specimen flaw by routing an increased portion of the driving flux through the resonator. A minor driving dipole is induced diameter-wise across the annular sensing face of the pick-up core (now called a resonator).
(2) Disposing the resonator annular air gap to a location longitudinally within the driving toroid winding window so that the resonant flux path is integrated into a portion of the driving toroid 455 (FIG. 9), integrated linkage to the pick-up coil is increased, drawing oscillatory energy from the orthogonal driving field of the window location.